PubMed · 5789193
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
S F Russo. 1969. Two fluorescence experiments.. https://doi.org/10.1021/ed046p374
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Small, single-module proteins that fold in a single cooperative step may be paradigms for understanding early events in protein-folding pathways generally. Recent experimental studies of the 64-residue chymotrypsin inhibitor 2 (CI2) support a nucleation mechanism for folding, as do some computer stimulations. CI2 has a nucleation site that develops only in the transition state for folding. The nucleus is composed of a set of adjacent residues (an alpha-helix), stabilized by long-range interactions that are formed as the rest of the protein collapses around it. A simple analysis of the optimization of the rate of protein folding predicts that rates are highest when the denatured state has little residual structure under physiological conditions and no intermediates accumulate. This implies that any potential nucleation site that is composed mainly of adjacent residues should be just weakly populated in the denatured state and become structured only in a high-energy intermediate or transition state when it is stabilized by interactions elsewhere in the protein. Hierarchical mechanisms of folding in which stable elements of structure accrete are unfavorable. The nucleation-condensation mechanism of CI2 fulfills the criteria for fast folding. On the other hand, stable intermediates do form in the folding of more complex proteins, and this may be an unavoidable consequence of increasing size and nucleation at more than one site.
Economic function of the exocrine pancreas is based on non-parallel synthesis, transport and secretion of pancreatic enzymes during basal state and postprandially. Reserve capacity of acinar cells is also augmented by adaptation to the diet as well as by regeneration. In mild pancreatic insufficiency complex dietetic considerations help to maintain the necessary secretory capacity of the pancreas. In severe cases effective substitution therapy is mandatory and increasing lipase survival by dietetic maneuvers, by optimizing trypsin and chymotrypsin levels as well as acid and bile secretion can significantly ameliorate results of replacement therapy of steatorrhea. However, in painful chronic pancreatitis high protease activities seem to be beneficial. Individual replacement therapy with pancreatin preparations adapted to the requirements of the patient has to be chosen in difficult cases.
The precursor homodimeric p66/p66 form of human immunodeficiency virus type-1 reverse transcriptase (HIV-1 RT) possesses the DNA polymerase and RNase H activities involved in the synthesis of the double-stranded provirus DNA. Reverse transcription is initiated from tRNALys in the case of HIV-1. The present study confirmed that interactions between HIV-1 RT and tRNALys induce protein conformational changes and demonstrated that these interactions stimulate the enzymatic activities associated with the p66 subunit. Thus, the p66/p66 form of the enzyme is strongly stimulated in both DNA polymerase and RNase H activities. Preincubation of the enzyme with tRNA is an obligatory step to obtain the stimulatory effect. The affinity of template, primer, or substrate for RT p66/p66 did not change when the enzyme was preincubated with tRNALys at stimulatory concentrations; the interaction of tRNA with p66/p66 has an effect only on the maximal rate of polymerization. It is further shown that the RNase H domain of RT is much more accessible to protease attack than the DNA polymerase active site.